[Bug rtl-optimization/97497] gcse wrong code generation with partial register clobbers

[krebbel at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97497

--- Comment #6 from Andreas Krebbel <krebbel at gcc dot gnu.org> ---
Alternatively I could also mark r12 as preserved across function calls for
-fpic in the backend. In fact all the bits we care about are preserved. Since
the register is fixed all the accesses do come from the backend itself.

That's similar to what I was trying with the fixed_regs hack. But I agree that
this might not be correct in general.

The full fix is probably to track the exact parts of partially clobbered regs
which stay live but this would be a major change.